Electronic warfare systems are used on modern military aircraft as part of their offensive and defensive capabilities. These electronic warfare systems emit RF signals that travel through space. Radar systems use RF emissions to locate and track opposing aircraft and some radar systems are incorporated within missiles to assist in the self-guided propulsion of a missile to its target. An electronic warfare search receiver is used defensively to detect those RF emissions. The receiver searches the range of frequencies (the RF spectrum) in which the RF emissions are likely to occur. The receiver then detects and analyzes the nature of the RF signals. By determining the characteristics of the signals received, the defender will know the nature of the threat and, for example, will know if a radar guided missile has "locked on" to the defenders aircraft. These systems are used in friendly as well as unfriendly aircraft. In a tactical or strategic environment, the number of aircraft and the density and diversity of the emissions in the RF spectrum is quite large and is expected to increase. Existing detection and monitoring equipment that use wide band search receivers will find the RF emissions difficult to successfully monitor in such an environment. For instance, on routine missions where airplanes are flying in a pattern, each plane will be emitting its own radar signal to look for hostile or unidentified aircraft. Simultaneously, each aircraft will have on its own search receiver and will be listening for radar signals emitted from other sources which could include hostile airplanes or missiles, ground sources or from ships at sea. The airplane will also receive radar signals from the other airplanes that are flying in its formation. It would be advantageous to identify these signals from the adjacent airplane and filter them out while at the same time listening for radar signals that are of more interest. There may be a variety of signals particularly in an electronically congested area that are of no or little interest. It would be desirable to eliminate these signals after they were identified as not being of interest.
Under certain circumstances, one particular type of waveform or several particular types of waveforms may be of keen interest to the pilot. Under these circumstances it may be advantageous to identify these signals quickly for further action.
Existing window addressable memories (WAM) are used to filter out unwanted signals or identify signals of particular interest. However, these types of filters have a limited window space such as 16 windows for identification of signals to be filtered out or identified for further processing. This type of device has inflexible parameters because parameters must be hard-wired at fixed resolution and range. This type of filter can only cover a limited number of discrete characteristics from the total range that can be covered by a pulse descriptor word (PDW).
It is unlikely that a single receiver type will be capable of meeting all offensive or defensive threat detection and analysis requirements dictated by the future electronic warfare environment. Instead, a set of search and analysis receivers of complimentary capabilities are likely to be required to meet future demands. Trade-offs between probability of intercept, bandwidth, simultaneous signal resolution, sensitivity, receiver complexity and power consumption are necessary. It would be advantageous to have the ability to identify and eliminate or mark for interest a large number of parameters of a pulse descriptor word and at the same time be able to change the requirements for identification as the environment changes.